A user context is a word having meanings. The user context is used as a word indicating all items of information on users. The user context is also used as a word indicating a place, an activity, and a state of a user at a certain point in time. In the present description, the user context is used as the latter meaning.
Conventionally, it has been often performed in the world of the world wide web (WWW) to detect the context of a user automatically and provide a service based on the detection results. For example, this service allows a user to write an appointment into an electronic schedule note so that an email is delivered on the day before the appointment so as not to miss the appointment.
However, since it is difficult to comprehend the context of the real world, at the present situation, such a service is performed only in limited fields. This is because such an infrastructure that a sufficiently large number of sensors are widely present is required in order to automatically comprehend the context of the real world using a computer or the like.
However, in recent years, this situation has been changed due to the development of apparatuses, called smart devices or smart appliances, which have a network function and can collect sensing information and a manipulation history and an operation history of the apparatuses.
When such smart apparatuses such as smart devices or smart appliances are sufficiently popularized among the people, the activity and situation (user contexts) of a user at a certain point in time can be estimated from information (the user's manipulation history of an apparatus or the sensing information) on the user collected from these smart apparatuses.
Although various services that use the estimated user contexts can be considered, one of the important services among them is a service that detects an event relating to a user that “things are not going properly” and takes measures against the event.
For example, Patent Document 1 discloses a technique of incorporating a sensor into a stick used by an elderly person so as to detect a contact between a stick and the ground and judging that “the elderly person is walking safely” if the stick and the ground make contact periodically and otherwise judging that “something dangerous has happened”. The system disclosed in Patent Document 1 aims to provide a caring service for elderly persons who are out for a walk using the judging results.
Similarly, Patent Document 2 discloses a technique of extracting sleeping hours, an activity quantity, an excretion frequency, and the like of a care recipient from sensors attached to the care recipient and issuing a warning when the extracted data indicates an abnormality in the living pattern of the care recipient. Moreover, Patent Document 3 discloses a technique of monitoring biological information such as an electrocardiographic signal of a user and automatically detecting an abnormality.
However, Patent Documents 1 to 3 require a further improvement.    Patent Document 1: Japanese Patent Application Publication No. 2006-85609    Patent Document 2: Japanese Patent Application Publication No. 2007-114830    Patent Document 3: Japanese Patent Application Publication No. 2005-253609